Prospective Study on Physical Activity and Risk of In Situ Breast Cancer
Menée auprès de 283 827 femmes incluses dans la cohorte EPIC, cette étude prospective évalue l'association entre la pratique d'une activité physique (activité professionnelle, domestique ou de loisir) et le risque de cancer invasif du sein (1 059 cas ; durée médiane de suivi : 11,7 ans)
Background: Physical activity has been identified as protective factor for invasive breast cancer risk, whereas comparable studies on in situ carcinoma are rare. Methods: The study included data from 283,827 women of the multinational EPIC-cohort study. Detailed information on different types of physical activity performed during the prior year, such as occupational, recreational, and household activity, as well as on important cofactors were assessed at baseline. Adjusted hazard ratios (HR) for in situ breast cancer were estimated by Cox proportional hazards models. Results: During a median follow-up period of 11.7 years, 1,059 incident breast carcinoma in situ were identified. In crude and adjusted multivariable models, no associations were found for occupational, household, and recreational physical activity. Furthermore, total physical activity was not associated with risk of in situ breast cancer. Comparing moderately inactive, moderately active and active participants with inactive study participants resulted in adjusted HRs of 0.99 (95%-CI 0.83-1.19), 0.99 (95%-CI 0.82-1.20), and 1.07 (95% CI 0.81-1.40), respectively (p-value of trend test: 0.788). No inverse associations were found in any substrata defined by age at diagnosis or BMI status. Conclusions: In this large prospective study, we did not find any evidence of an association between physical activity and in situ breast cancer risk. If not by chance, the contrast between our results for carcinoma in situ and the recognized inverse association for invasive breast cancer suggests that physical activity may have stronger effects on proliferation and late stage carcinogenesis.